A Gary, Indiana, police officer was shot and killed while on duty Sunday -- his 47th birthday -- prompting some of his colleagues to come into work on their day off to help with the manhunt for the shooter.

Officer Jeffery Brady Westerfield was found by a citizen unresponsive in a parked squad car just before 6 a.m. near 26th Avenue and Van Buren Street, according to Chief Wade Ingram.

"It is a tremendous loss to the department," said 5th District Councilwoman Kimberly Robinson.

Officials said they are following up on several leads in the investigation.

"Any loss of life, particularly a police officer's loss of life, is devastating to a department, is devastating to a community and what it means is we will to go through every legal measure to make sure that the person who is responsible for this is held accountable," said Gary Mayor Karen Freeman-Wilson.

Gun violence in the area had been declining with shootings down by more than 50 percent, until a spike in homicides occurred about a week ago, officials said.

"The fact that an officer has lost his life certainly causes you to question whether you can make the type of headway that needs to be made to ensure ultimate success," said Freeman-Wilson. "We know that we can push back on this."

The last time an officer was killed while on-duty in the area was 1998, Freeman-Wilson said.

Ingram said the Lake County Sheriff's Department was leading the investigation into Westerfield's death with the assistance of the Gary police department and other agencies. He said several officers were coming in on their day off to help with the manhunt.

"You can never be too careful as an officer," Ingram said. "Every day you put that uniform on your life is on the line."